1. Field of the Invention
The invention relates to the field of coating processes. More particularly, the invention relates to a plural direction application of coating materials by simultaneously applying fiber and binder from different sources. In still greater particularity, the invention relates to a spray application of refractory fibers to a surface with an alpha alumina crystal forming binder. By way of further characterization, but not by way of limitation thereto, the invention is a method for applying refractory fibers with an aluminum chloride binder.
2. Description of the Prior Art
Spray application of refractory fiber is a desirable method for producing a refractory material in furnaces, kilns, and other thermally insulated structures. Advantages of such a method include reduced costs and reduced down time for a furnace or the like. That is, as opposed to previous methods of relining furnaces, requiring either manual replacement of brick or mechanically attaching refractory fiber linings, spray insulation may be easily and quickly applied to the surfaces. A number of spray methods and applications have been previously disclosed. However, none of these previous methods or applications result in a refractory lining which adheres to the substrate upon which it is applied and remains there during thermal cycling and exposure to elevated temperatures of 2200.degree. F. or more.
One example of a prior method for applying refractory fiber is disclosed in U.S. Pat. No. 4,547,403 issued on Oct. 15, 1985. The method disclosed in that patent utilizes an aluminum phosphate based binder. While suited for its intended purpose, this method suffers from the limitation that the refractory layer sprayed upon a substrate surface may debond from that substrate upon thermal cycling. That is, while the method may result in bonding of the refractory fiber one to another, the bond between the fiber-binder layer and the substrate upon which it is sprayed may be deficient. That patent also discloses a colloidal alumina-clay binder which suffers from the same weak bond line at the substrate interface.
Another method for applying refractory insulations utilizes refractory fibers and a hydraulic setting-inorganic binder. This product is marketed under the trademark CERAMOSPRAY.RTM. which is a registered trademark of the U.S. Mineral Products Company. While suited for its intended purpose, this method utilizes a dry cementitious binder which is limited in its temperature range to a stated maximum of 2200.degree. F. In addition, a cementitious binder such as calcium aluminate or calcium phosphate may adversely affect silicate based brick products at temperatures in excess of 2000.degree. F., thus effectively reducing the maximum service temperatures of these cementitious refractory materials in such applications. Mechanical anchors are also required with this method. While suited for its intended purpose, such a system would be unsuitable for use in high temperature applications and may be unsuitable for applications in which a refractory lining is sprayed onto a brick substrate. Since the majority of furnaces and kilns are brick lined, such a system may find little application in these areas.
Still another spraying method is disclosed in U.K. Patent application Nos. 2,093,014 and 2,093,015. These applications utilize phosphate bonding and suffer from the limitations discussed above with other phosphate bonding agents. In addition, these applications disclose a system utilizing a dry composition which is more difficult to control in a spray method than applicants' liquid binder.
Still another spray application method is disclosed in Japanese Pat. Nos. 51-40846 and 49-87723. These references disclose the use of dry alumina cement the amount of which must be limited to avoid very high densities thereby affecting the thermal insulating properties of the layer. In addition, as stated in those references, when used in large quantities the scattering of cement dust creates an undesirable pollution problem. While the use of colloidal alumina is disclosed, it is only disclosed with a dry material such as bentonite to give it bonding characteristics. Such a system may suffer from weak bonding at the substrate interface.
Finally, another sprayable ceramic fiber insulation system marketed under the trademark FIBERBRAX.RTM., a trademark of the Sohio Engineered Materials Company (CARBORUNDUM) is a sprayable system which is rated to a maximum temperature of 2100.degree. F. While suited for its intended application, the system is limited in temperature application and is also a silica based binder material which is subject to debonding at the substrate interface as with the clay and phosphate binders. In addition, this is a two part system in which the fiber is pre-coated thus potentially suffering from the dry binder separation limitations discussed above. To improve the bonding of the layer to the substrate, mechanical anchors are recommended for many applications. As can be appreciated by one skilled in the art, the use of anchors increases cost and furnace down time. Anchors are also unsuitable for a badly deteriorated brick or other substrate since attachment of the anchors to the substrate may be difficult and/or dangerous.